Process for the manufacture of nodular cast iron

ABSTRACT

The invention relates to a casting process for the production of castings of nodular cast iron. Molten flake iron is poured into the casting mould by way of an intermediate cavity which contains the nodularising agent.

United States Patent Dunks et a1.

Nov. 28, 1972 [54] PROCESS FOR THE MANUFACTURE OF NODULAR CAST IRON [72] Inventors: CliffordM. Dunlu; James L. lVk- Caulay, both of Reigate, England [73] Assignee: Materiak and Nkthock United,

Reigate, Surrey, England [22] Filed: July 16, 1969 [21] Appl. No.: 842,204

[30] Foreign Application Priority Data July 17, 1968 Great Britain ..33,970/68 [52] US. Cl. ..l64/57, 75/130, 164/72, 164/59, 164/133, 164/363, 164/358 [51] Int. Cl ..B22d 27/18, B22d 27/20 [58] Field of Search ..164/55, 57, 58, 59, 321, 319, 164/304, 72, 80, 133, 107; 75/58 [56] References Cited 3,514,285 5/1970 Baklrerus ..l64/55X FOREIGN PATENTS OR APPLICATIONS 255,994 1 1/1962 Australia [64/72 743,121 l/1956 Great Britain ..164/133 I 1,132,055 10/ 1968 Great Britain ..164/55 1,132,056 10/ 1 968 Great Britain ..164/55 1,901,366 8/1970 Germany ..164/5S 1,936,153 8/1970 Germany ..1 64/55 OTHER PUBLICATIONS Chill Elimination in Ductile Iron by Mold Inoculation," by Dell, W. J., and Christ, R. J., Modern Casting, July ]964 pp. 408-416.

Primary Examiner-Robert D. Baldwin Assistant Examiner-V. K. Rising Attomey-Woodling, Krost, Granger 8: Rust ABSTRACT The invention relates to a casting process for the production of castings of nodular cast iron. Molten flake iron is poured into the casting mould by way of an intermediate cavity which contains the nodularising agent.

3 Claim, 3 Drawing Figures PROCESS FOR THE MANUFACTURE OF NODULAR CAST IRON This invention relates to an improved process for the production of nodular or spheroidal graphite cast iron castings.

In the past few years a number of methods have been developed to nodularize molten grey iron as it runs from the melting furnace or when it is received in the ladle from which the castings are to be poured.

All of these methods depend upon the use of certain nodularizing alloys such as magnesium, calcium, lithi v um, strontium, barium, cerium, didynium, lanthanum and yttrium, which are readily oxidizable at the temperature of the molten cast iron or are volatile and where their effect tends to disappear either during processing or subsequent standing and time taken in transference to the molds. The consequence of this is loss of strength properties as the iron reverts to the original flake form. A common foundry terminology applied to this phenomena is fading and this fading is a common problem in the industry.

To correct this, a number of steps are taken, one of which is to use a large quantity of nodularizer; another is to make a further addition during the process of pouring; another is to inoculate the iron either in the ladle or during the process of pouring. All of these however, add up to increased cost in manufacture, for these nodularizing alloys are expensive, and rarely is there a recovery of more than 40 percent possible, further the excessive quantities of nodularizing alloys tends to give rise to the formation of oxides or silicates which become entrapped in the melt producing dirty castings or dross defects. They may also give rise to sub-surface blowholes and elephant skin, and may intensify shrinkage of the molten iron during solidification giving rise to shrinkage and other defects causing loss of both physical properties, and confidence in the finished product.

A further problem is that most of these alkali metals or rare earth metals such as cerium, didynium, lithium, magnesium and strontium are also carbide stabilizers, hence there is also the inherent problem of over-treatment, the production of hard and brittle castings, and loss of machinability and ductility.

According to this present invention, it is now possible to overcome most of these problems, and at the same time reduce the cost of manufacture. This has been achieved by effecting the nodularizer addition within or adjacent to the mold itself.

In addition to the usual pouring bush, downsprue, gating and risering systems required correctly to introduce the metal to the casting shape, provision is made for a pre-formed chamber which may be described as the intermediate chamber to contain the nodularizing alloy. This intermediate chamber maybe located in any suitable position relative to the pouring bush, downsprue, gating and risering system, or the casting mold itself, in such a manner that the incoming molten metal comes into contact with the nodularizer and the reaction commences uniformly. The reaction then continues progressively until the mold is completely filled.

Accordingly the present invention provides a process for the production of nodular or spheroidal graphite cast iron castings in which untreated molten grey cast iron is introduced into the mold by way of one or more 2 intermediate chambers containing a nodularizing agent in an amount sufficient to convert the graphite to nodular or spheroidal form.

The invention also provides a mold for use in the process of the inventionwhich comprises a pouring bush, downsprue, gating and risering systems and a casting mold cavity wherein there is provided one or more intemiediate chambers associated with the mold and arranged in the path of the molten metal entering the mold, which chamber or chambers is adapted to receive a nodularizing agent. I

Where it is desired to form complex castings itmay be necessary to have more than one inlet for molten metal into the casting mold, in which case an intermediate chamber canbe associatedwith any or all of the systems feeding the molten metal to the casting mold, for example an intermediate chamber can be associated with each runner bar.

Due to .the fact that the reaction commences immediately the molten metal covers the nodularizer, solution occurs out of contact with air. Thus in this embodiment of the invention, the temperature lossduring the pouring of the casting is negligible and loss due to volatilization and oxidation are completely eliminated.

A further advantage of the invention is that it is possible to control precisely the amount of nodularizer that is required for a given weight of metal to convert the graphite from flake to nodularform. This then eliminates the previous dangers due to dross inclusions and over-treatment.

For example complete conversion of the graphite form from flake to perfect spheroidal shape has been achieved with as little as 0.15 per cent of the nodularizer alloy used in accordance with the invention. With any of the conventional techniques previously employed, it would have been necessary to use at least 0.75 per cent additive. This represents an important saving, for these alloys are the most costly ingredients used in the manufacture of nodular iron. V

In thisprocess, any of the well known nodularizing reagents or mixtures may be used; there is a complete absence of turbulence, fume, or pyrotechnics and sound and dense castings are assured.

The nodularzing reagents may be employed in lump form, as crushed aggregate, in powderform, or as extruded or compacted/bonded shapes. The size and shape of the nodularizer particles and the quantity required will, as can readily be understood by one skilled in the art, depend upon a number of parameters including the size and shape of the chamber, rate of flow of molten metal through the chamber, ferrostatic pressure, metal temperature and composition, weight and type of casting, and method of manufacture.

One embodiment of the invention is illustrated in the accompanying drawings in which FIG. 1 is a plan view of the face of a mold for a sliding block with the cover of the mold removed,

FIG. 2 is an enlarged sectional view of that part of the mold shown in FIG. 1 containing the downsprue, intermediate chamber and dam and outlet to the riser taken generally in the direction of the arrow II; and

FIG. 3 is a plan view of FIG. 2.

Referring now to the drawings, the mold as illustrated is for the casting of a sliding block. The actual casting mold for the block is shown as l. Molten metal enters thecasting mold by way of a pouring bush, not shown, downsprue 2, intermediate chamber 3, riser 4 and riser neck 5. Nodularizing agent, in an amount calculated on the basis of the parameters referred to above is placed in the intermediate chamberwhich is provided with a'dam 6 to regulate flow and to ensure sufficient residence time of the metal in the intermediate chamber. The mold box is represented by reference '7 As molten. iron passes into the casting mold 1 it contacts the nodularizing additive in the intermediate chamber 3 and the graphite in the iron is converted into nodular or spheroidal form.

The following Examples serve to illustrate this invention.

EXAMPLE I A ladle of untreated molten grey cast iron having a tensile strength of 14.4 tons per square inch was taken to pour a series of automobile flywheel castings.

All the molds were identical in every respect, having an intermediate chamber formed and located directly beneath the downsprue. The quantity of nodularizer reagent required (in this case the alloy constituted 55 percent silicon, 4 percent magnesium, and the balance of iron) was calculated based on 0.35 per cent of the combined weight of the casting, the runner bar, ingate, and the feeder riser the total weight being 85 lbs. i.e. 4.76 ozs. of nodularizing reagent was used, in this instance in the form of )6 inch X /4 inch lumps.

The molds were thenpoured in sequence, taking l2 minutes to dispose of all themetal. There was no turbulence during pouring, in fact no evidence of fume or flame was observed.

On subsequent examination, all the castings contained uniform graphite spheroids in a matrix entirely free from carbide. The castings were solid throughout and possessed a superior skin finish that had hitherto been considered possible. The ultimate properties of the treated iron were Tensile strength 52.8 tons per square inch; Elongation 4 percent.

EXAMPLE 2 In another treatment series, a ladle of untreated grey cast iron, of 14 tons per square inch tensile, was used to pour a series of diesel engine crankshafts.

In this case the intermediate chamber was enlarged to fit the flask in which the mold was made, and the amount of nodularizer was calculated based on the EXAMPLE 3 4 The composition and properties of the untreated flake ironusedwas:

Total carbon In this instance, the intermediate chamber was constructed separately in the form of a core assembly and was located outside the mold proper. The intennediate chamber was enclosed except for the metal inlet point with apouring bush placed over this, and the exitwas located directly over the downsprue of the mold. This method was proved useful where there is insufficient space within the molding box to provide for a suitable intemiediate chamber'or where large castings are to be poured or where complex castings and gating and risering systems are involved.

Fifty cwts. of this iron was used to pour a cooling segment casting with 0.7 percent of a calcium magnesium ferro siliconalloy located in the external intermediate chamber.

The casting was poured and the visual observations were exactly as in the preceding Examples. After cooling and examination, the casting was sound in every respect with the graphite converted to the fully nodular form. The casting was a cooling segment, and its properties after processing were:

Tensile strength 56.2 tons per sq.inch

Elongation 4% and on testing proved to be uniformly solid throughout.

We claim:

1. A process for the production of spheroidal graphite cast iron castings in which molten cast iron of such composition that it would be a gray cast iron with the graphite in flake form if cast under normal foundry conditions, for example in a sand mold, is introduced into a mold by way of a mold inlet and travels to a mold cavity by way of a gating system which gating system includes at least one intermediate chamber, a nodularizing agent being present in said at least one intermediate chamber in an amount sufficient to convert the graphite to spheroidal form, said molten cast iron contacting said nodularizing agent in said at least one intermediate chamber as it travels from said mold inlet to said mold cavity.

2. A process as claimed in claim 1, wherein said intennediate chamber is fluidly connected to a part of the gating system selected from the group of mold parts in the mold consisting of the pouring bush, sprue, runner bar, spinner, ingate and feeding riser.

3. A process as claimed in claim 1, wherein said nodularizing agent is selected from the group of materials consisting of magnesium, lithium, barium, cerium, didynium, lanthanum and yttrium.

seas: 

2. A process as claimed in claim 1, wherein said intermediate chamber is fluidly connected to a part of the gating system selected from the group of mold parts in the mold consisting of the pouring bush, sprue, runner bar, spinner, ingate and feeding riser.
 3. A process as claimed in claim 1, wherein said nodularizing agent is selected from the group of materials consisting of magnesium, lithium, barium, cerium, didynium, lanthanum and yttrium. 